The invention generally relates to headphones that are designed to provide noise attenuation.
There are at least three headphone design types, which are generally categorized in terms of how they are worn by the user. The three design types are referred to as around-the-ear in-the-ear, and on-the-ear designs. Around-the-ear headphones have large earphones that resemble earmuffs. Like earmuffs, the around-the-ear earphone covers and surrounds the ear. They typically provide very good noise attenuation but they are not particularly comfortable, especially for people using eyeglasses. Since the earphone surrounds the user""s ear, it cuts off air circulation behind the ear and thus can be uncomfortably warm in hot weather.
Under some circumstances, the around-the-ear of headphones actually provide too much noise attenuation. There are environments or applications in which it is in fact desirable to hear some external sound, for example, in certain industrial applications and in airplanes. In large industrial plants where a lot of machine noise is present, it may be useful to use radios as a way of communicating with coworkers located elsewhere in the plant. Because of the high noise levels, earphones must be worn to hear the radio communications. To be effective, the earphones must also block out some of the external noise. But if they block out too much of the external noise, the user will not be able to hear the conversations of nearby coworkers or the helpful sound queues of operating machinery. In airplanes, the airline pilot needs headphones that effectively block out the external engine noises. But the pilot also needs to hear the conversation of people who are nearby, such as their copilot or other airline support staff. In those applications, the around-the-ear headphones sometimes work to well.
The in-the-ear headphone which typically provides less attenuation than the around-the-ear type has an ear piece that fits into the ear cavity, i.e., concha. Unlike the around-the-ear design, the in-the-ear headphone is typically very light and compact. For some people, they are also very comfortable. A significant number of other people, however, are either unwilling to insert an earpiece into their ear because they have sensitive ears or they (e.g. children) have an ear size that is not large enough to accommodate the ear piece. For that group of people, the in-the-ear design is not appropriate.
The third design (i.e., the on-the-ear design) is less intrusive than the other two. According to this design, also referred to as the supra aural design), each earphone has a cushion that simply rests on the ears when the headphone is being worn by the user. Typically, the cushion is made of an open cell foam material that easily transmits sound. This design tends to be lightweight, compact, and very comfortable. One disadvantage, however, is that conventional on-the-ear designs do not very effectively attenuate external noise. Thus, they are not well suited for use in noisy environments.
In general, in one aspect, the invention is a supra aural headphone including an earphone, which includes a shell body, a cushion mounted on the shell to thereby define an internal cavity behind the cushion, and an acoustical driver mounted within the internal cavity which during use reproduces sound when driven by an audio signal. The cushion has a passageway extending therethrough so as to acoustically connect the internal cavity with a user""s ear cavity when the cushion is resting on the user""s ear while being worn by the user. The internal cavity has a total volume that is larger than about 10 cubic centimeters so as to passively attenuate any external sound which leaks through the earphone to the user""s ear cavity, and the acoustical driver is mounted within the internal cavity in such a way as to avoid obstructing the passageway which acoustically connects the internal cavity with the user""s ear cavity.
In preferred embodiments, the total volume of the internal cavity is substantially larger than about 10 cc, e.g. an order of magnitude larger than 4 cc. The cushion has a back side and a front side and the passageway forms an opening in the front side having a diameter that is less than about 15 mm in size (e.g. within a range of about 10 to 15 mm). The passageway increases in diameter as it passes through the cushion from the front side to the back side. The internal cavity is partially filled with an acoustic damping material. The driver is offset from the central axis of the passageway (e.g. it lies completely off of the central axis). The driver lies in a plane that is inclined with respect to the central axis.
Preferred embodiments also include an acoustical microphone mounted within the internal cavity, which during use provides a feedback signal for an active noise reduction circuit. The microphone is mounted in front of the driver and offset from the center of the driver. More specifically, the microphone lies in a first plane and the driver lies in a second plane and the first plane is substantially perpendicular to the second plane. Also, the passageway forms an opening in the back side of the cushion and the second plane (i.e., the driver plane) is inclined with respect to the opening in the back side of the cushion so that the microphone extends into the passageway.
Also in preferred embodiments, there is a driver support structure which defines a smaller cavity behind the driver when the driver is assembled onto the support structure. The smaller cavity is within and separate from the first-mentioned cavity and it is acoustically isolated from the first-mentioned cavity except for a pressure equalization hole interconnecting them. In addition, a wall of the smaller cavity is formed by a portion of the shell body which also includes a hole connecting the smaller cavity to outside of the shell body. The hole connecting the smaller cavity to the outside is covered by an acoustically resistive screen. The cushion is made of a molded, self skinned, damped, compliant material.
In general, in another aspect, the invention is a supra aural headphone including an earphone that includes a shell body having an inside and an outside; and a cushion mounted on the shell. The cushion and the inside of the shell defines an internal cavity behind the cushion. The cushion includes a passageway extending therethrough so as to acoustically connect the internal cavity with a user""s ear cavity when the cushion is resting on the user""s ear while being worn by the user. The internal cavity has a total volume that is larger than about 10 cubic centimeters.
In general, in yet another aspect, the invention is a supra aural headphone including an earphone, that includes a shell body, a cushion mounted on the shell to thereby define an internal cavity behind the cushion, an acoustical driver mounted within the internal cavity which during use reproduces sound when driven by an audio signal, and an acoustical microphone mounted within the internal cavity, which during use provides a feedback signal for an active noise reduction circuit. The cushion has a passageway extending therethrough so as to acoustically connect the internal cavity with a user""s ear cavity when the cushion is resting on the user""s ear while being worn by the user. The internal cavity has a total volume that is larger than about 4 cubic centimeters. The acoustical driver is mounted within the internal cavity in such a way as to avoid obstructing the passageway which acoustically connects the internal cavity with the user""s ear cavity.
The supra aural (on-the-ear) configuration provides comfortable, lightweight and easy to use headphones which attenuate ambient noise and reproduce high quality signals. Noise attenuation is achieved by both passive and active means. Passive attenuation is achieved by using very soft, self skin, highly damped foam cushions and by using a large volume cavity behind the cushion. Active attenuation is achieved by acoustic feedback methods.
Headphones designed in accordance with the invention provide flat attenuation of about 15-20 db over a broad frequency range. This is sufficient to significantly attenuate external noise but not so much as to block all sound such as the conversation of a nearby person. In addition, such headphones are also considerably smaller and lighter than alternative designs which provide comparable attenuation.
Since they rest on the ear without compressing the ear against the head, the back of the ear remains exposed to circulating air thereby resulting in better heat dissipation. Thus, the headphone of the present invention offers attenuation characteristics comparable to the around-the-ear designs but without the discomfort in hot weather.
Other advantages and features will become apparent from the following description of the preferred embodiment and from the claims.